Extracted from Harry Potter: The Creature Vault by Jody Revenson
Dementors, spectral Dark creatures that guard Azkaban, are sent to Hogwarts to find and bring back Sirius Black in Harry Potter and the Prisoner of Azkaban. Harry is deeply affected by their soul-draining power, so Professor Lupin teaches him the Patronus charm to shield himself. In Harry Potter and the Order of the Phoenix, Dementors attack Harry and Dudley Dursley in Little Whinging, but Harry manages to drive them away. Dementors fight on Voldemort’s side in Harry Potter and the Deathly Hallows – Parts 1 and 2.
Dementors are ethereal, insubstantial creatures with no perceptible structure. The visual development artists on Harry Potter and the Prisoner of Azkaban designed a veiled, skeletal shape that could suggest some anatomical frame when the Dementors glided or hovered in the air, and swathed them in shroud-like black robes that hung from their skulls. The creature designers worked closely with the costume department, who experimented with an assortment of fabrics that could convey a floating effect. Typically filmed in lowly lit scenes, the Dementors’ colouration could not be solely black or else they would disappear into the background, so a combination of dark greys and blacks was used. The designers referenced embalmed bodies, whose wrappings were rotting and coming off, and added overlaid textures to the Dementors that gave the appearance of layers of decay.
The Dementors do not talk and only needed a mouth-like opening to drain happiness from their victims, so movement was the key to communicating these chilling, menacing characters. The filmmakers had hoped to bring the Dementors to life with a practical effect. They shot tests of fabric-covered Dementor models using different wind and lighting effects, and ran the film backward or in slow motion, but were not satisfied with the results. A puppeteer was brought in to test the same ideas, this time in an underwater environment, in hopes of portraying a slow and forceful creature. These tests captured what the filmmakers envisioned, but it was realised that using this process would make it difficult to repeat the same motion. It was decided that the Dementors needed to be computer-generated. The footage of the underwater tests was an important reference tool, and the digital artists expanded upon it with effects that gave the Dementors their own realistic gravity, making them stealthy and unearthly.